Some suspect that the sudden increase in winter art came about because of something called the "little ice age" which may have occurred from 1300 to 1900. This cooling period featured three minima, each with a following warm break. Great famines, increased warfare, and plagues all took place in this time period. Some say that this period, also called the age of nightmares, got that name from the constant fires, poor home ventilation, and from beds surrounded by sheets for warmth. The lack of fresh air may have caused vivid dreams and nightmares.